1. Field of the Invention
The present invention relates to an electronic clinical thermometer for detecting temperature by arranging a temperature sensitive resistor within a thermometric oscillator circuit and counting the oscillation frequency, and in particular, to an electronic thermometer adapted to reducing power consumption.
2. Description of the Prior Art
A prior art electronic clinical thermometer in general use is equipped with a sliding switch for controlling the turning on and off of the power source, and the power is shut off by operating the sliding switch after the detection of temperature. However, operating such a sliding switch is troublsome, and power is often wasted due to the operator forgetting to turn off the power.
Moreover, a temperature sensitive resistor is installed in the circuit of a thermometric oscillator whose oscillation frequency varies with temperature. The resistance of the resistor is small so that a large current flows through the resistor, consuming large power. Accordingly, the wasted amount of power due to keeping the power in the on-state during the period for which no operation is needed, has been largely responsible for determining the life of the battery. Further, the electronic clinical thermometer in general used is mainly used under the emergency condition in which somebody in the family is having a fever. In that condition, there exists a possibility of finding it inoperative during such an emergency because of the dead battery due to the last user forgetting to turn off the switch. Moreover, in the case of use in a hospital, if the power consumption is large, there is a high possibility of having a dead battery due to high frequency of use.
In order to avoid the dead battery situation due to power exhaustion, there has been proposed a thermometer in which a switching transistor for controlling the turning on and off of the power source is installed in the LSI for the clinical thermometer and so arranged as to have the power source to be turned off automatically after elapse of a prescribed time (for example, the times for detecting and displaying the temperature) to eliminate the possiblity of forgetting to turn off the switch.
However, the switching transistor for controlling the turning on and off of the power source is disadvantageous because it occupies a large area on the LSI chip, thus defeating attempts to make a small-size and low-price LSI.
In addition, in the case where the time for reading out the temperature display is uncertain, like in the hospital, the time interval between initiating taking of temperature in the room and the nurse coming to record the measured temperature is relatively large. Under these circumstances, it is difficult to shorter the time between turning the power source on to shutting the power source off automatically, because of the possible of having the power source turned off before the temperature display is read out. Therefore, many electronic clinical thermometer are utilized without the function of automatically shutting off the power source, and hence, the only method for reducing the power consumption is to turn off the power switch consciously at time right after readout.